1. Field of the Invention
This invention relates to a magnetic disc for high density recording in which coercive force has been improved, such as, for example, a magnetic disc for in-plane recording used for hard disc drive, or the like.
2. Description of the Related Art
In magnetic discs mounted in a hard disc system, etc. used for external memory device of computer, etc., attempt has been made to allow the wavelength of a recording signal to be shorter with implementation of high density recording of information. Moreover, with such implementation of high density recording, improvement in output-to-noise ratio, i.e., signal-to-noise ratio (S/N) of reproduction signal is one of important tasks to be attained.
In magnetic discs, for the purpose of improving the S/N, improvement in reproduction output and lowering of medium noise are required. First, in order to improve reproduction output, particularly in the case where wavelength of a recording signal is short, it is effective to employ a method in which coercive force of medium is improved to thereby reduce magnetic transition width (transition width in magnetization) at the time of recording signals thus to reduce interference between reproduction waveforms. On the other hand, for the purpose of lowering medium noise, it is said that it is effective to lower exchange bonding strength between magnetic fine particles within the magnetic layer. In addition, it is known that lowering of exchange bonding strength between magnetic fine particles is confirmed as lowering of coercive force rectangular ratio of medium.
In recent years, as an effective method for attaining, at the same time, improvement in medium coercive force and reduction of exchange interaction between magnetic fine particles, there have been proposed a method in which introduction gas such as Ar, etc. is caused to have higher pressure of the order of 2.about.3 Pa in sputtering a thin film magnetic layer including Co, etc. as major component onto a non-magnetic substrate to micro-crystallize magnetic fine particles sputtered, a method in which a non-magnetic intermediate layer is provided within a magnetic layer to allow the magnetic layer to be of stacked structure, and the like.
As a medium in which magnetic layer is caused to be of staked structure, many media in which non-magnetic intermediate layer such as Cr, etc is provided within a magnetic layer comprised of Co--Ni--Cr, Co--Cr--Ta, or Co--Pt--Cr, etc. have been reported until now. However, it could not be said that sufficient coercive force has been ensured with such media.